This invention relates to data storage systems and more particularly to the reading of information from a rotating medium.
The data storage density of the magnetic and optical recording systems has increased dramatically. Presently most systems use run-length limited (RLL) coding and peak detection (PD) to achieve high reliability and high storage densities. More advanced techniques consisting of partial response (PR) signaling and maximum-likelihood sequence detectors (MLSD) or Viterbi detectors allow further increases in density.
While the MLSD or Viterbi detector provides an effective way to recover data from a readback signal, a Viterbi detector without an equalizer is usually too complex to implement, since the complexity of a Viterbi detector grows exponentially with the number of encoded cells which are interfering with one another.
In the past separate equalizer circuits were used for both the timing extraction and data recovery functions. Use of separate equalizers allows the timing function and the data recovery function to be optimized separately; however, two separate equalizers consume roughly twice the power of one equalizer. If only one equalizer is used, a tradeoff is required in one of the functions resulting in a less than desirable performance for the other function.
What is needed in the art is a low cost and lower power system which is optimized for both the data recovery and the timing extraction functions.